The Advanced Television Systems Committee (ATSC) published a Digital Television Standard in 1995 as Document A/53, hereinafter referred to simply as “A/53” for sake of brevity. Annex D of A/53 titled “RF/Transmission Systems Characteristics” is particularly incorporated by reference into this specification. A/53 describes vestigial-sideband amplitude modulation of the radio-frequency carrier wave using an eight-level modulating signal, which type of over-the-air DTV broadcasting is called “8VSB”. In the beginning years of the twenty-first century efforts have been made by some in the DTV industry to provide for more robust transmission of data over broadcast DTV channels without unduly disrupting the operation of so-called “legacy” DTV receivers already in the field. Robust transmission of data for reception by mobile and hand-held receivers is provided for in a Candidate Standard: ATSC Mobile DTV Standard published in June 2009, referred to hereinafter simply as “A/153” for sake of brevity, and incorporated herein by reference. A/153 is directed to transmitting ancillary signals in time division multiplex with 8VSB DTV signals, which ancillary signals are designed for reception by mobile receivers and by hand-held receivers. The ancillary data employ internet protocol (IP) transport streams. The ancillary data are randomized and subjected to transverse Reed-Solomon (TRS) forward-error-correction (FEC) coding before serially concatenated convolutional coding (SCCC) that uses the ⅔ trellis coding of 8VSB as inner convolutional coding.
The operation of nearly all legacy DTV receivers is disrupted if ⅔ trellis coding is not preserved throughout every transmitted data field. Also, the average modulus of the signal should be the same as for 8-VSB signal as specified in the 1995 version of A/53, so as not to disrupt adaptive equalization in legacy receivers using the constant modulus algorithm (CMA).
Another problem concerning “legacy” DTV receivers is that a large number of such receivers were sold that were designed not to respond to broadcast DTV signals unless de-interleaved data fields recovered by trellis decoding were preponderantly filled with (207, 187) Reed-Solomon forward-error-correction (RS FEC) codewords of a specific type or correctable approximations to such codewords. Accordingly, in order to accommodate continuing DTV reception by such legacy receivers, robust transmissions are constrained in the following way. Before convolutional byte interleaving, data fields should be preponderantly filled with (207, 187) RS FEC codewords of the type specified in A/53.
This constraint has led to the M/H data encoded for reception by mobile and hand-held DTV receivers being encapsulated within (207, 187) RS FEC codewords of the general type specified in A/53, differing in that they are not necessarily systematic, with the twenty parity bytes located at the conclusions of the codewords. The twenty parity bytes of some (207, 187) RS FEC codewords appear earlier in the codewords to accommodate the inclusion of training signals in the fields of interleaved data. The 207-byte RS FEC codewords invariably begin with a three-byte header similar to the second through fourth bytes of an MPEG-2 packet, with a thirteen-bit packet-identification (PID) code in the fourth through sixteenth bit positions. Except for the three-byte header and the twenty parity bytes in each (207, 187) RS FEC codeword, the remainder of the codeword is available for “encapsulating” 184 bytes of a robust transmission.
A/153 prescribes successive equal lengths of the M/H data stream being subjected to transverse Reed-Solomon (TRS) coding and then to periodic cyclic-redundancy-check (CRC) coding to develop indications of the possible locations of byte errors in the TRS coding. These procedures are designed to correct byte errors caused by protracted burst noise, particularly as may arise from loss of received signal strength, and are performed in apparatus called an “M/H Frame encoder”. The output signal from the M/H Frame encoder is supplied for subsequent serial concatenated convolutional coding (SCCC) of the general sort described by Valter Benedetto in U.S. Pat. No. 5,825,832 issued 20 Oct. 1998 and titled “Method and device for the reception of symbols affected by inter-symbol interface”. The encoder for the SCCC comprises an outer convolutional encoder, an interleaver for bit-pairs generated by the outer convolutional encoder, and an inner convolutional encoder constituting the precoder and ⅔ trellis coder prescribed by A/53.
In A/153, the parity bytes generated by the TRS coding are transmitted at the conclusion of 187 successive equal lengths of the M/H data stream used for generating them. TRS coding of M/H data frames extends over 968-millisecond intervals of 8VSB signals. A/153 offers three options for the TRS coding. A/153 permits M/H transmissions to use (211, 187), (223, 187) or (235, 187) TRS coding. The inventor observed that the use of three different lengths of TRS codewords complicates the efficient packing of M/H data frame for one or two of these options. The inventor presumed that the three different lengths of TRS codewords were used in order to accommodate a transport stream composed of fixed-size 187-byte-long MPEG-2-compatible packets, but perceived that such accommodation was unnecessary for the IP transport stream, which uses packets of indeterminate length. The inventor discerned that just one codeword length could be used for all TRS coding options to be offered for a prescribed size of RS Frame, which would facilitate efficient packing of RS Frames of that size.
An initial portion of the TRS coding procedure in the M/H Frame encoder can be analogized to a matrix-type block interleaving procedure of the following sort. A first framestore is written row by row with respective successive equal lengths of the M/H data stream and then read column by column to the Reed-Solomon coder, which generates successive TRS codewords. A final portion of the TRS coding procedure in the M/H Frame encoder can be analogized to a matrix-type block de-interleaving procedure of the following sort. A second framestore is written column by column row by row with respective successive TRS codewords and then read row by row to reproduce respective successive equal lengths of the M/H data stream followed by TRS parity bytes.
In a receiver for M/H signals, turbo decoding of the SCCC'd M/H signal is followed by a TRS decoding and error-correction procedure. An initial portion of the TRS decoding procedure in an M/H Frame decoder can be analogized to a matrix-type block de-interleaving procedure of the following sort. A first framestore is written row by row with respective successive equal lengths of the M/H data stream and ensuing TRS parity and then read column by column to the Reed-Solomon decoder, which generates successive corrected TRS codewords. A final portion of the TRS decoding procedure in the M/H Frame decoder can be analogized to a matrix-type block re-interleaving procedure of the following sort. A second framestore is written column by column row by row with respective corrected TRS codewords and then read row by row to reproduce respective successive equal lengths of error-corrected M/H data stream. The second framestore can be smaller than the first since only the data bytes of the corrected TRS codewords need to be subjected to the block re-interleaving procedure.
The memory for storing RS Frames in the M/H Frame decoder of a DTV receiver is sizable. The inventor discerned there would be a substantial reduction in memory if a single framestore were used both for the matrix-type block de-interleaving procedure to provide TRS codewords to the RS decoder and for the matrix-type block re-interleaving procedure for reproducing M/H data with corrections. The inventor observed that, in order that this can be done, the reading out of error-corrected previous M/H data row by row had to be completed before over-writing by new M/H data.
The M/H Frame decoder in a DTV receiver receives equal-length CRC codewords from a turbo decoder. Turbo decoding involves iterative decoding procedures that are not strictly real-time in nature. The more time that can be allotted to the turbo coding procedures, the less power those procedures are likely to consume. Confining the M/H-encapsulating (MHE) packets of a Group to just the first 118 transfer stream (TS) packets in a 156-TS-packet Slot tends to leave a time interval for performing the TRS decoding operations. The convolutional byte interleaving employed in 8VSB DTV broadcasting causes various delays of the bytes of the 118 TS packets in a Slot, spreading them out over 170 segments of 8VSB data fields. This reduces the time available for performing the TRS decoding operations and re-writing the RS Frame framestore with corrected bytes before it receives new data for over-writing the previous content. To lengthen the time for performing turbo decoding procedures and the subsequent TRS decoding procedures, it is customary for an M/H service to be received just in every fourth one of the M/H Groups that can be transmitted. Most of this time is used for iterated turbo decoding procedures, with the TRS decoding procedure performed in no more than one 8VSB frame interval. The inventor perceived that there is a simple way to extend the time interval for performing the TRS decoding operations. Such extension is beneficial when a single framestore is used both for the matrix-type block de-interleaving procedure to provide TRS codewords to the RS decoder and for the matrix-type block re-interleaving procedure for reproducing M/H data with corrections. The time interval for performing the TRS decoding operations can be extended by transmitting the MHE packets encapsulating portions of the equal-length CRC codewords containing TRS parity bytes before transmitting the MHE packets encapsulating portions of the equal-length CRC codewords containing M/H data bytes. This is because the portion of the framestore used to store TRS parity bytes does not need to be read row by row before being over-written by new TRS parity bytes. The only reading of the TRS parity bytes after their being written row by row into the framestore is the column by column reading to the RS decoder. Each of the TRS codewords used in M/H Frame encoding per A/153 has at least 24 TRS parity bytes extracted from as many MHE packets. Accordingly, the time interval for performing the TRS decoding operation can be extended by at least a factor of 211/187 or almost 1.13.
The M/H transmission system as originally proposed by LG Electronics was designed to transmit an MPEG-2-compatible stream of 187-byte transport packets. However, in ATSC subcommittees it was decided that A/153 should specify that M/H transmissions use internet-protocol (IP) transport packets of indeterminate length. It was subsequently determined that under certain conditions the Fast Information Channel (FIC) when operated according to its original design provided insufficient capability for conveying information. At least one proposal was made to augment the information capacity of the FIC with information from IP packets transmitted in the SCCC. The inventor discerned that augmenting the FIC information with information from IP packets transmitted in the SCCC would lead to undesirable complications in receiver design, which complications could be avoided simply by increasing the capability of the FIC for conveying information. The inventor proposed doubling the number of bytes of FIC in each Chunk to create extended FIC Chunks to double the information capacity of the FIC, doubling the number of FIC Segments in each M/H Group to permit repeating the FIC as often as originally proposed. That is, the inventor proposed extended FIC-Chunks that had 74 times NoG bytes, NoG being the number of M/H Groups in one-fifth of an M/H Frame. However, in an alternative approach to accommodating extended FIC-Chunks, A/153 was amended to specify that FIC-Chunks can be extended in duration and transmitted less frequently in each M/H Frame in order to increase the information capacity of the FIC. This alternative approach avoided SCCC being partly taken up by information for supplementing FIC information. This alternative approach also reduced the need to revise designs of signaling hardware in both transmitters and receivers. The drawback of this alternative approach is possible increase in the times receivers will require to acquire a newly selected channel.